1. Field of the Invention
The present invention deals with novel branched ether ester compounds useful as viscosity index modifiers. These esters are derived from novel branched ether alcohols. It is because of the internal location of the branched ether group in these ether esters that these materials are very efficient viscosity index modifying materials. They have low viscosity, are stable to oxidation and exhibit minimal variation in viscosity as a function of temperature. All of these properties are required for a viscosity index modifier.
2. Description of the Art and Practices
Viscosity index modifiers are known in the art. Typical teachings are as follows:
U.S. Pat. No. 4,207,196, to Sudekum issued June 10, 1980 teaches that ethylene/alpha olefin polymers are useful in viscosity index modification.
U.S. Pat. No. 4,212,816 to Hentschel issued July 15, 1980, teaches that pentaerythritol esters of carboxylic acids are useful as viscosity index modifiers.
U.S. Pat. No. 4,181,618 to Durand issued Jan. 1, 1980, teaches that graft copolymers of vinyl compounds are useful as viscosity index modifiers.
U.S. Pat. No. 4,63,159 issued April 1981 to Berens et al teaches that certain aliphatic polyol compounds reacted with branched monocarboxylic acid form esters useful in automatic transmission fluids.
None of these materials shown to be useful as viscosity index modifiers are as effective as the highly branched ether esters taught by the current invention.
There are several factors known about liquidity in esters. When made to a given molecular weight, the highest viscosity esters are those derived from saturated linear alcohols. This class of compounds also exhibit a wide change in viscosity as a function of temperature. It is for these reasons that esters derived from saturated linear alcohols are least desirable as viscosity index modifiers.
Pentaerythritol, a highly branched four hydroxyl group containing alcohol is sometimes used to obtain an improvement in viscosity over saturated alcohols. The improvement is only partial and there are difficulties in controlling the reaction if less than four equivalents of acid is added.
The next improvement is to base the ester upon oxo alcohols. Oxo alcohols are well known to those skilled in the art. They contain about 20-30% branching at the alpha position. The branching is methyl. Esters derived from this type of raw material are the more liquid than esters derived from saturated linear alcohols if the esters have the same molecular weight.
Finally, esters based upon guerbet alcohols are the most liquid of the groups discussed. There are many references to the use of gurebet alcohols to make esters for use in a variety of lubricating applications. The useful property of guerbet alcohols in lubricating applications is the beta branch and the liquidity it renders.
Guerbet Alcohols are known materials which have a high degree of regiospecific beta branching. They have been known since the 1890's when Marcel Guerbet first synthesized them. (M. Guerbet, C. R. Acad. Sci. Paris, 128, 511; 1002 (1899)). These materials are high in molecular weight and are liquid to very low temperatures. The guerbet reaction gives very specific branching in the alcohol as shown; ##STR1##
As can be seen by the above reaction the molecules have substitution on the second carbon from the hydroxyl group. This branching has been found to be critical to the preparation of a product having the desired lubrication and oxidative stability properties. If the branching were on the same carbon as the hydroxyl group, the hydroxyl group would be a secondary one and would be very hindered and has low reactivity. As one moves the branch position away from the beta carbon, the liquidity, lubricity and metal substantivity decreases. If the branch is lower alkyl like methyl in some oxo alcohols, there is little increase in the liquidity, lubricity and metal substantivity over normal alcohols having the same number of carbons. Additionally, the oxo process gives only some beta branching (between 1 and 28%) the guerbet process gives essentially 100% product.
U.S. Pat. No. 4,425,458 issued January 1984 to Lindner et al teaches that certain diesters of guerbet alcohols are useful as lubricants in polycarbonate applications. Additionally, U.S. Pat. No. 4,767,815 issued August 1988, to O'Lenick teaches that certain guerbet ether esters are likewise useful as polycarbonate lubricants.
U.S. Pat. No. 4,800,077 issued January 1989, to O'Lenick et al teaches that guerbet alcohols can be used to prepare certain conditioning quaternary compounds.
U.S. Pat. No. 4,868,236 issued September 1989, to O'Lenick teaches that certain guerbet alcohol citrate esters are useful in plastic lubrication.
U.S. Pat. Nos. 4,731,190 and 4,830,769 both to O'Lenick teaches that certain alkoxylate esters are useful as lubricants useful in facilitating the working of metal. Guerbet alcohol derived esters have not enjoyed widespread acceptance in viscosity index modification applications.
Surprisingly, the compounds of the present invention are superior to esters of guerbet alcohols of the same molecular weight. Hence they are very useful as viscosity index modifiers.